For a long time already the thermal energy of geothermal thermal water or thermal sole from aquifers is utilized. Underground layers of water-bearing permeable rock known as aquifers are found at various depths in the earth's crust in various geologic formations. Besides of thermal water, aquifers often also comprise gas deposits. Due to the high pressure in these depths the gas is dissolved in the thermal water and such a solution herein is termed aquifer fluid. The gases dissolved in the thermal water in general are combustible gases, the isolated energetic and chemical utilization of which is not profitable from an economic point of view. The gases dissolved in the thermal water comprise methane and other gaseous hydrocarbons, hydrogen and/or carbon monoxide as well as not combustible components such as water vapor and/or carbon dioxide. Upon production of the aquifer fluid, the gas expands, is expelled from the solution and has to be blown off or flared, thereby emitting climate relevant gases—unless it is used.
With todays drilling technology boreholes to deep aquifers can be produced so that aquifer fluid with initial temperatures of more than 60° C. can be produced from depths of up to several kilometers. Besides of using it for heating of buildings, the thermal water is also used for the generation of electricity. After the energetic utilization, the cooled thermal water is recirculated into the aquifer by means of a recirculation device.
As can e.g. be seen from “Improved utilization of low temp thermal water rich in hydrocarbon gases” by Bašić et al., GHC Bulletin, Summer 1990, in the past aquifer fluid comprising therein dissolved gas was pretreated prior to using the thermal energy. Thereby methane was separated from the aquifer fluid by means of a gas separation device. The energy of the thermal water was used in a device for using the thermal energy and the energy of the separated methane was made available by a subsequent combustion process. This combustion process on the one hand comprises the combustion of the separated methane in a gas engine with thereto connected generator for electricity generation, on the other hand the utilization of the heat energy obtained by the direct combustion of the methane for further heating the obtained thermal water. After utilization of the energy of the thermal water and the methane, the cooled thermal water is reinjected into the aquifer, whereby the energy needed for reinjection has been obtained by the methane combustion. By this method the energy comprised in the aquifer fluid is well but not optimally used.
The combustion of the methane according to Bašić generates flue gases so that this otherwise environmental friendly use of the inner energy of the aquifer fluid, due to the released flue gases, results in an environmental pollution similar to flaring.
In addition, today many crude oil deposits are already exploited and the still existing crude oil amounts can only be produced with enhanced effort which makes a (cost) efficient production method desirable. These deposits are extensively filled with water so that they are suitable aquifers in the sense of the present invention.
Due to the production method using water injection not only significantly exploited but also quite new crude oil deposits are suitable aquifers.